Photonic crystals are a new class of man-made materials. They are often referred to as “metamaterials.” Photonic crystals are formed by dispersing a material of one dielectric constant periodically within a matrix having a different dielectric constant. A one-dimensional photonic crystal is a three-dimensional structure that exhibits periodicity in dielectric constant in only one dimension. Bragg mirrors are an example of a one-dimensional photonic crystal. To form a Bragg mirror, alternating thin layers having different dielectric constants and refractive indices are stacked on top of one another. The combination of several thin layers forms a three-dimensional structure that exhibits periodicity in dielectric constant in only the direction orthogonal to the planes of the thin layers. No periodicity is exhibited in either of the two dimensions contained within the plane of the layers.
A two-dimensional photonic crystal can be formed by periodically dispersing rods or columns of a material of one dielectric constant within a matrix having a different dielectric constant. Two-dimensional photonic crystals may exhibit periodicity in dimensions perpendicular to the length of the rods, but no periodicity is exhibited in the direction parallel to the length of the rods.
Finally, a three-dimensional photonic crystal can be formed by periodically dispersing small spheres or other spatially confined areas of a first material having a first dielectric constant within a matrix of a second material having a second, different, dielectric constant. Three-dimensional photonic crystals may exhibit periodicity in dielectric constant in all three dimensions within the crystal.
Photonic crystals may exhibit a photonic bandgap over a range of wavelengths in directions exhibiting periodicity in dielectric constant. In other words, there may be a range of wavelengths of electromagnetic radiation that will not be transmitted through the photonic crystal in the directions exhibiting periodicity in dielectric constant. This range of wavelengths that are not transmitted is known as a photonic bandgap of the photonic crystal. No photonic bandgap is exhibited in directions that do not exhibit periodicity in dielectric constant.
When defects are introduced into the periodic dielectric structure of a photonic crystal, localized electromagnetic modes may be allowed at wavelengths within the photonic bandgap. For example, resonant cavities have been formed in photonic crystals by introducing point defects into the periodic dielectric structure, and waveguides have been formed in photonic crystals by introducing line defects into the periodic dielectric structure.
Photonic crystal devices that include waveguides have been provided with gain material to provide light emitting devices. Such light emitting devices are useful in optical communication and optical information processing applications. However, a significant quantity of electromagnetic radiation generated by gain material in known light-emitting photonic crystal devices is not effectively coupled to the waveguide.